Asset size alone isn't really enough to indicate what the appropriate BSA staff count is. Staffing would depend on the unique risk presented by a Bank's clients, products, services, etc. I've seen a one person BSA Department and BSA Departments with thousands of resources, both of which are staffed appropriately. It may be helpful to do a staffing analysis to support the downsizing you referenced.
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"100 victories in 100 battles isnt the most skillful. Subduing the other's military w/o battle is the most skillful." Sun-Tzu